Amended review of Antique Electronics Supply K-502 Stereo Amplifier

Jstas

I finally got a set of speakers that really show this amplifier up.



That's it and here is a link to the specs:

K-502 Specs


Anyway, I was at George's house last night auditioning speakers from his abundant stash. I was fearing not being able to find anything decent that this amplifier could power well enough. Boy was I wrong! This amplifier handled every set of speakers we threw on there with aplomb. I still have not been able to push its limits. The transformers for the speaker channels have never even heated up with 8 ohm loads and being driven at literally 100% volume levels. Yes, 100% volume levels. I was powering my dad's Electrro-Voice speakers with this amplifier and my brother and I were listening to the cleanest and clearest sound I have ever heard from any amplifier running balls-to-the-wall, all out like that.

I am going to create enclosures for a pair or Pioneer 4 ohm speakers and see if I can push the amp with a 4 ohm load.

I also mentioned previously that the potentiometer for the volume control might be bad. While I still think it is, I do believe that a good portion of the noise is due to the signal source. I have been using a Sony Car-Discman and the signal seems to be dirty. I hooked the amp up to a CD Changer George had last night. I think it was a JVC, I can't remember. However, there was considerably less noise than with the Discman and it leads me to believe that the Discman is a dirty source. I will have to find a CD player for this system. Maybe a cheap pre-amp and tuner too?

As for the amplifier itself, I have seen iffy reviews concerning this amps quality levels. I have to wonder if those who are disappointed with the amplifier have assembled it well or even correctly. It is a very efficient design and it is very clean. Much cleaner than I thought it ever could be. Especially since I put it together myself. I have to say that this amplifier, for $140 and a couple hours worth of your time is one hell of a steal. Defintly a diamond in the rough. If anyone is looking for a cheap amp for any reason, this is certainly one to consider. I am becoming more and more pleased with it as I play with it. I can't wait to get home from work and play with it some more with the speakers I grabbed from George last night.

gidrah

Good to hear. I've got it high on my list. I even picked up a new soldering iron. I'll wait 'til after the Mid-West Audio Fest to decide.

Tour2ma

Thanks for the update Jstas. I'll bet it eats up those 4-ohms without maxing the output.

George Grand

That amp made those KLH 17's sound better than I've ever heard before. I drove them with all kinds of Dynaco stuff when they were in Stephie's bedroom, and the tube amp cleaned the Dynaco stuffs clock. A credit to Henry Kloss, and JStas. Talented men.

That cd player was a JVC John. Temperamental thing no?

George Grand (of the Jersey Grand's)

RuSsMaN

This is starting to make my pants go crazy. I'm looking to setup my first 2ch tube rig in the not-so-distant future.

Jstas, lets act like this is an AMF model airplane, what skill level would you set this at for assembly? Additionally, are the tubes socketed, or soldered right to the board? What did you mount to, a project box, scrap piece of mdf/pine?

If that amp made some vintage 17's shine (and I trust the ears that reported this), that gives me hope for the Advent Legacy's I plan on using. I'm guessing the volume pot is passive, due to the lack of gain you reported on some sources. I can deal with that later though.

Cheers,
Rooster

Jstas

Questions questions questions...

First off, the kit comes with everything you need. Including a nice piece of poplar to mount the parts to. I didn't finish the mounting board but I want to build an enclosure for the amp anyway, with a plexiglas window so you can still see the tubes glow!

The tubes are socketed but you need to solder the sockets to the board. Really, not all that difficult. The tubes can be removed otherwise, when a tube blows, your whole deal is shot to hell. It can be a real pain trying to unsolder 9 connections simultaneously.

The skill level needed for this project? On a typical hobbist scale of 1-5, 5 being most difficult, I'd rate it a 3. It was incredibly easy for me but I have a good deal of background in electronics so I have to rate it conservativly for fear of making less experienced hobbyists overly confident in tackling a project that may be over a head or two. Eventhough it is comparatively cheap for an amplifier, 140 bucks is still a good chunk of change to waste by **** up a project. You will need soldering skills. A tad bit of experience doing basic circuit board construction/repair will go a long way too. The skill level may be as low as a 2 but again, my skill level is probably a 5 so it was easy for me. There are very detailed directions with pictures and a chart for identifying resistors and capacitors and such too. So that is not an issue. The major difficulty is solid construction. Like I said, I have read not so shining reviews for this unit but I have to believe that those reviewers either didn't assemble the unit well/properly or they are using a really bad signal source.

The volume pot is grounded and has a power lead to it too. Its a standard piece that you can find for anything needing variable resistance like a volume knob. As far as the lack of gain, I would not blame it on the amp. The only pre-amp function it has is the volume knob so it acts more like a gain level adjustment than a volume knob. I noticed the biggest gains when I went to better equipment and the DVD player with the digital source. When I get the Onkyo pre-amp, I'll be able to play with it more.


I would imagine that the Advent Legacys would work well with this amp. They are along the same kind of lines as the KLH speakers and I do believe that they are acoustic suspension. If that is the case then I would expect similar performance.


Oh, and I don't think we really need to know what is going on in your pants! :eek:

gidrah

I've seen the link for the company that actually makes the kit (not AES). There's a cage you can get and maybe some other things too. I've also seen pics of this amp where people have put some time and effort into the case/base. When done right it'll look like a $3k amp.

Tour2ma

gidrah, got links? Aren’t you the one that plexi’d his PC?

Originally posted by Jstas
Questions questions questions...

Oh you love the attention... so here's a little more...

I want to build an enclosure for the amp anyway, with a plexiglas window so you can still see the tubes glow!

Heat/ ventilation concerns come into play? Any guidelines in the instructions? I do like the Plexiglas idea... I think raife is the one that did this to his PC's case.

It can be a real pain trying to unsolder 9 connections simultaneously.

For future reference... Solder-Up... it's a little roll of braided material that wicks molten solder up in a flash. Easy as pie to use... and works better than pie, too

There are very detailed directions with pictures and a chart for identifying resistors and capacitors

Being color blind is a big hurdle for me with resistor ID.... "Is that red-green-red or green-red-green???"

I noticed the biggest gains when I went to better equipment and the DVD player with the digital source. When I get the Onkyo pre-amp, I'll be able to play with it more.

I hadn't flashed to the fact that you did not have a pre-amp in any of the set-ups you've been using... interesting.

Oh, and I don't think we really need to know what is going on in your pants! :eek:

NOW THAT'S THE CLUB SPIRIT... Don't get mad... get even... BTW I second the motion, but Russ will tell us anyway. Just one, or in this case three, of the things he's proud of...

George,
When you compared this little tube-job to Dynaco, were you talking about Dynaco SS or tube amps?

George Grand

Both. I drove them with a SS SCA-80Q integrated, still in Stephie's bedroom driving a pair of "The New Advent Loudspeaker" from 1979, AND with a really ratty looking tube ST-70 that was electronically okay. I don't have the ST-70 anymore, I traded it for a pair of Polk RTA11TL's, and I don't have those anymore either. Sold them to finance the purchase of my AR-9's.

Just realized I have over 600 posts. Time to cut back a little. Too much exposure can be a bad thing.

George Grand (of the Jersey Grand's)

Tour2ma

Thanks George, I've been sniffing around ST-70's on ebay and I'll rethink now, if this little number out did them.

Jstas

Originally posted by Tour2ma
Heat/ ventilation concerns come into play? Any guidelines in the instructions? I do like the Plexiglas idea... I think raife is the one that did this to his PC's case.

Yes, I thoughgt of that. I will most likely use a perforated metal plate on the backing and maybe a decorative vent on the top of the amplifier itself. I was also considering a pair of PC fans to move air across the amp. Either with the screwed to the sides or mounted on the perforated metal plate in the back.

Originally posted by Tour2ma
For future reference... Solder-Up... it's a little roll of braided material that wicks molten solder up in a flash. Easy as pie to use... and works better than pie, too

I wasn't worried about removing it. I woldn't even use Solder-Up, just heat it up and pul it out of the hole. Worry about the solder later. What I'm worried about is over-heating not only the socket but the board. I don't know if you have even seen what happens when overheat a printed circuit but it goes down the doard like a fuse. Not to mention the board itself can melt and cause leads that aren't supposed to touch to touch and that's bad. Mmmmkay?

Originally posted by Tour2ma
I hadn't flashed to the fact that you did not have a pre-amp in any of the set-ups you've been using... interesting.

Well, the amplifier has a pre-amp. It's just a volume control though so no signal processing abilities. The volume control behaves more like a gain control with volume response dropping off as you go higher in volume.

George Grand

Tour,

Don't limit your horizons on account of my report. Awful lot of ST-70 lovers out there. I'm just a man.

Somebody said you picked up a pair of Carver Amazing Platinum's. Is that so?

George Grand (of the Jersey Grand's)

Tour2ma

George,

I’m still considering an ST-70 and will likely nail one. I just won't be as aggressive knowing there's a good, economical tube option to test drive. I actually “won” an original configuration auction yesterday, but did not meet reserve, which the seller offered me, but I declined. Price was just too high for an original set with untested, very old tubes.

Issue I’ve found with the 70’s is there's so much tweaking going on, I can't be sure of what I am getting. I was also high bidder, but didn't meet reserve on a heavily modified one that I'm still considering. Have traded a number of e-mails with the seller and I've gotten nothing, but good vibes from him. I owe him an answer by Tuesday.

Yes, I picked up a pair of original CA's a couple weeks ago. So as to not hijack the thread I’ll post some initial impressions over in the “Speakers” area. See you over there.

BTW you back home now? How's the sunburn? :cool:


Jstas,
Yup, I've damaged boards trying to pull multi-pin transistors with the old heat, tug and wiggle technique. My experience with Solder Up has been all good. Mentioned it on the off chance you had no experience with it.

gidrah

I haven't plexi'ed anything. I think it was Goingganzo. Plexi & blue neon.

I have a Dynaco ST-70 that was updated by a previous owner. It sounds pretty good. Not great from what I've heard, but haven't listened to it that much. I'm working a swing shift and don't want to wake the family. Some people swear by the stock version, others swear by the various mods they've done. Someday I'll mod, but 'til then I'm still quite happy with it.